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1 Supplementary information doi: /nchem.366 Geometric and Electronic Structure and Reactivity of a Mononuclear Side-On Nickel(III)-Peroxo Complex Jaeheung Cho 1, Ritimukta Sarangi 2, Jamespandi Annaraj 1, Sung Yeon Kim 1, Minoru Kubo 3, Takashi Ogura 3, Edward I. Solomon 2,4 * and Wonwoo Nam 1 * 1 Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic Systems, Ewha Womans University, Seoul , Korea 2 Stanford Synchrotron Radiation Laboratory, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA 3 Picobiology Institute, Graduate School of Life Science, University of Hyogo, Hyogo , Japan 4 Department of Chemistry, Stanford University, Stanford, CA 94305, USA *Corresponding authors: wwnam@ewha.ac.kr, edward.solomon@stanford.edu 1 nature chemistry 1

2 Experimental Section Materials and Instrumentation. All chemicals obtained from Aldrich Chemical Co. were the best available purity and used without further purification unless otherwise indicated. Solvents were dried according to published procedures and distilled under Ar prior to use S1. H 18 2 O 2 (90% 18 O-enriched, 2% H 18 2 O 2 in water) and 18 O 2 (95% 18 O- enriched) were purchased from ICON Services Inc. (Summit, NJ, USA). The 12-TMC (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) ligand was prepared by reacting excess amount of formaldehyde and formic acid with 1,4,7,10-tetraazacyclododecane S2. [Ni(14-TMC)(O 2 )] + (2) and [Mn(14-TMC)] 2+ (4) were prepared according to the literature methods S3,S4. [Ni(12-TMC)(CH 3 CN)](ClO 4 ) 2 was prepared by reacting Ni(ClO 4 ) 2 6H 2 O (0.86 g, 2.63 mmol) with 12-TMC (0.50 g, 2.19 mmol) in CH 3 CN (50 ml). The mixture was refluxed for 12 h. After cooling, solvent was removed under vacuum to give a purple solid, which was collected by filtration and then washed with methanol several times to remove remaining Ni(ClO 4 ) 2 6H 2 O. Yield: 0.90 g (78%). ESI MS in CH 3 CN (see Supplementary Fig. S1B): m/z for [Ni(12-TMC)] 2+, m/z for [Ni(12- TMC)(CH 3 CN)] 2+, and m/z for [Ni(12-TMC)(ClO 4 )] +. UV-vis spectra were recorded on a Hewlett Packard 8453 diode array spectrophotometer equipped with a UNISOKU Scientific Instruments for low-temperature experiments or with a circulating water bath. Electrospray ionization mass spectra (ESI MS) were collected on a Thermo Finnigan (San Jose, CA, USA) LCQ TM Advantage MAX quadrupole ion trap instrument, by infusing samples directly into the source using a manual method. The spray voltage was set at 4.2 kv and the capillary temperature at 80 C. Resonance Raman spectra were obtained using a liquid nitrogen cooled CCD detector 2 nature chemistry 2

3 (CCD OPEN-1LS, HORIBA Jobin Yvon) attached to a 1-m single polychromator (MC-100DG, Ritsu Oyo Kogaku) with a 1200 groovs/mm holographic grating. An excitation wavelength of nm was provided by a He-Cd laser (Kimmon Koha, IK5651R-G and KR1801C), with 15 mw power at the sample point. All measurements were carried out with a spinning cell (1000 rpm) at 20 o C. Raman shifts were calibrated with indene, and the accuracy of the peak positions of the Raman bands was ±1 cm -1. Product analysis was performed with an Agilent Technologies 6890N gas chromatograph (GC) and Thermo Finnigan (Austin, Texas, USA) FOCUS DSQ (dual stage quadrupole) mass spectrometer interfaced with Finnigan FOCUS gas chromatograph (GC- MS). EPR spectra were obtained on a JEOL JES-FA200 spectrometer. 1 H NMR spectra were measured with Bruker DPX-250 spectrometer. Crystallographic analysis was conducted with an SMART APEX CCD equipped with a Mo X-ray tube at the Crystallographic Laboratory of Ewha Womans University. Generation and Characterization of [Ni(12-TMC)(O 2 )] + (1). Treatment of [Ni(12- TMC)(CH 3 CN)](ClO 4 ) 2 (3) (4 mm) with 5 equiv H 2 O 2 in the presence of 2 equiv triethylamine (TEA) in CH 3 CN (2 ml) afforded the formation of a green solution. [Ni(12- TMC)( 18 O 2 )] + was prepared by adding 5 equiv H 18 2 O 2 (32 L, 90% 18 O-enriched, 2% H 18 2 O 2 in water) to a solution containing 3 (4 mm) and 2 equiv TEA in CH 3 CN (2 ml) at ambient temperature. ESI MS in CH 3 CN (see Supplementary Fig. S3A): m/z for [Ni(12-TMC)(O 2 )] +. Crystals suitable for X-ray crystallography were obtained by using CH 3 CN/Et 2 O (vapour diffusion). The spin state of 1 was determined using the modified 1 H NMR method of Evans at room temperature S5-S7. A WILMAD coaxial insert (sealed capillary) tubes containing the 3 nature chemistry 3

4 complexes (60 L, 10 mm) dissolved in acetonitrile-d 3 (with 1.0% TMS) was inserted into the normal NMR tubes containing the blank acetonitrile-d 3 solvent (with 0.1% TMS) only. The chemical shift of the TMS peak in the presence of the paramagnetic metal complexes was compared to that of the TMS peak in the outer NMR tube. The magnetic moment was calculated using the following equation, = ( T / 2 fm ) where f is the oscillator frequency (MHz) of the superconducting spectrometer, T is the absolute temperature, M is the molar concentration of the metal ion, and v is the difference in frequency (Hz) between the two reference signals S7. 1/ 2 X-ray Crystallography. Single crystals of 1-(ClO 4 ) CH 3 CN and 3-(ClO 4 ) 2 were picked from solutions using a nylon loop (Hampton Research Co.) on a hand made cooper plate mounted inside a liquid N 2 Dewar vessel at ca. 40 ºC and mounted on a goniometer head in a N 2 cryostream. Data collections were carried out on a Bruker SMART AXS diffractometer equipped with a monochromator in the Mo K ( = Å) incident beam. The CCD data were integrated and scaled using the Bruker-SAINT software package, and the structure was solved and refined using SHEXTL V 6.12 S8. Hydrogen atoms were located in the calculated positions for 1-(ClO 4 ) CH 3 CN. Due to the high degree of disorder, however, hydrogen atoms could not be placed in ideal positions for 3-(ClO 4 ) 2. Crystal data for 1-(ClO 4 ) CH 3 CN: C 14 H 31 ClN 5 NiO 6, Orthorhombic, Pca2(1), Z = 4, a = (16), b = (6), c = (14) Å, V = (3) Å 3, = mm 1, calcd = g/cm 3, R 1 = , wr 2 = for 3915 unique reflections, 249 variables. Crystal data for 3- (ClO 4 ) 2 : C 14 Cl 2 N 5 NiO 8, Tetragonal, P4nmm, Z = 2, a = 8.969(3), b = 8.969(3), c = (11) Å, V = (11) Å 3, = mm 1, calcd = g/cm 3, R 1 = , wr 2 = 4 nature chemistry 4

5 for 889 unique reflections, 58 variables. The crystallographic data for 1- (ClO 4 ) CH 3 CN and 3-(ClO 4 ) 2 are listed in Table S1, and Table S2 lists the selected bond distances and angles. CCDC for 1-(ClO 4 ) CH 3 CN and for 3-(ClO 4 ) 2 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (+44) ; or deposit@ccdc.cam.ac.uk). X-ray Absorption Spectroscopy. The Ni K-edge X-ray absorption spectra of 1 and 2 were measured at the Stanford Synchrotron Radiation Laboratory (SSRL) on the focused 16-pole 2.0 T wiggler beam line 9-3 under standard ring conditions of 3 GeV and ma. A Si(220) double crystal monochromator was used for energy selection. A Rh-coated harmonic rejection mirror and a cylindrical Rh-coated bent focusing mirror were used. The solid sample for 1 was finely ground with BN into a homogeneous mixture and pressed into a 1-mm aluminum spacer between X-ray transparent 37 m Kapton tape. The solution samples for 2 (~120 L) were transferred into 2 mm delrin XAS cells with 37 m Kapton tape windows at 0 C. Both solid and solution samples were immediately frozen after preparation and stored under liquid N 2. During data collection, the samples were maintained at a constant temperature of 15 K using an Oxford Instruments CF 1208 liquid helium cryostat. Data were measured to k=16 Å -1 on 1 (transmission mode) by using an ionization chamber detector and to k=14 Å -1 on 2 (fluorescence mode) by using a Canberra Ge 30-element array detector. Internal energy calibration was accomplished by simultaneous measurement of the absorption of a Ni-foil placed between two ionization chambers situated after the sample. The first inflection point of the foil spectrum was fixed 5 nature chemistry 5

6 at ev. Data presented here are 2-scan (1) and a 7-scan (2) average spectra, which were processed by fitting a second-order polynomial to the pre-edge region and subtracting this from the entire spectrum as background. A four-region spline of orders 2, 3, 3 and 3 was used to model the smoothly decaying post-edge region. The data were normalized by subtracting the cubic spline and assigning the edge jump to 1.0 at 8340 ev using the Pyspline program S9. Theoretical EXAFS signals (k) were calculated by using FEFF (macintosh version 8.4) S10-S12 and the crystal structure of 1 and a structural model of 2 based on the DFT geometry optimized structure. The theoretical models were fit to the data using EXAFSPAK S13. The structural parameters varied during the fitting process were the bond distance (R) and the bond variance 2, which is related to the Debye-Waller factor resulting from thermal motion, and static disorder of the absorbing and scattering atoms. The nonstructural parameter E 0 (the energy at which k=0) was also allowed to vary but was restricted to a common value for every component in a given fit. Coordination numbers was systematically varied in the course of the fit but were fixed within a given fit. Electronic Structure Calculations. Gradient-corrected, (GGA) spin-unrestricted, broken-symmetry, density functional calculations were carried out using the ORCA S14,S15 package on a 32-cpu linux cluster. The Becke88 S16,S17 exchange and Perdew86 S18 correlation non-local functional was employed to compare the electronic structure differences between 1 and 2. The coordinates obtained from the crystal structure of 1 were used as the starting input structure for 1. For 2, the crystal structure of a monomeric [Ni(14- TMC)] 2+ species was modified to a [Ni(14-TMC)O 2 ] + starting input structure. The core properties basis set CP(PPP) S19,S20 (as implemented in ORCA) was used on Ni and the 6 nature chemistry 6

7 Ahlrichs all electron triple- TZVP S21,S22 basis set was used on all other atoms. Populations were obtained using a Mulliken Analysis (MPA). Wave functions were visualized and orbital contour plots were generated in gopenmol S23,S24. Compositions of molecular orbitals and overlap populations between molecular fragments were calculated using the QMForge S9. EXAFS Analysis. A comparison of the k 3 weighted Ni K-edge EXAFS for 1 and 2 S25 along with their non-phase shift corrected Fourier transforms (k= Å -1 ) is shown in Fig. S4. FEFF fits to the data are presented in Fig. S5 and S6 and Table S4. On going from 2 to 1, the first shell Fourier transform peak intensity increases and shifts to lower R. This indicates a decrease in first shell bond distances and an increase in coordination number in 1. FEFF fits to the data for 1 are consistent with 2 Ni-O interactions at 1.87 Å and 4 Ni-N interactions; 2 at 2.01 Å and 2 at 2.12 Å. The second shell for 1 is fit with single and multiple-scattering components from the macrocyclic ligand (see Table S4). Best-fits to the data of 2 resulted in metrical parameters similar to those published earlier S3. The first shell was fit with 1 Ni-O contribution at 1.93 Å and 4 Ni-N contributions at 2.12 Å. Fits to the second shell required splitting of the Ni-C single scattering contributions and required the inclusion of multiple scattering contributions arising from 12 C atoms consistent with a cisorientation of the four methyl groups (see Fig. S6 and Table S4). Reactivity Studies of 1. All reactions were run in an 1-cm UV cuvette by monitoring UV-vis spectral changes of reaction solutions, and rate constants were determined by fitting the changes in absorbance at 400 nm. Reactions were run at least in triplicate, and the data reported represent the average of these reactions. Complex 1 was prepared by reacting 3 with 5 equiv H 2 O 2 in the presence of 2 equiv TEA. The intermediate 1 (4 mm) was then 7 nature chemistry 7

8 used in reactivity studies, such as the oxidation of 2-phenylpropionaldehyde (2-PPA) at 25 ºC (see Supplementary Fig. S8), cyclohexanecarboxaldehyde (CCA) at 10 ºC (see Supplementary Fig. S9), and para-substituted benzaldehydes (para-y-ph-cho; Y = Me, F, H, Br, Cl) at 25 ºC (see Supplementary Fig. S10), under stoichiometric conditions in CH 3 CN. The purity of substrates was checked with GC and GC-MS prior to use. After completion of the reactions, products were analyzed by injecting reaction solutions directly into GC and GC-MS. Products were identified by comparing with authentic samples, and product yields were determined by comparison against standard curves prepared with authentic samples and using decane as an internal standard. The O 2 -transfer reactions were carried out by adding appropriate amounts of [Mn(14- TMC)] 2+ (4) to 1 (1 mm) in acetone at low temperature (i.e., 50 o C) to follow kinetics (see Supplementary Fig. S12), since the peroxo ligand transfer was fast at higher temperature. All reactions were run in an 1-cm UV cuvette by monitoring UV-vis spectral changes of reaction solutions, and rate constants were determined by fitting the changes in absorbance at 453 nm. The O 2 -transfer from 1 to 4 was further confirmed by taking ESI MS of the reaction mixture. Mixing equimolar amounts of 1 and 4 resulted in a decrease in the mass signal corresponding to 1 (m/z 318 for [Ni(12-TMC)(O 2 )] + ) with a concomitant increase in the signals corresponding to 5 (m/z 343 for [Mn(14-TMC)(O 2 )] + ) and 3 {m/z 143 for [Ni(12-TMC)] 2+ and 163 for [Ni(12-TMC)(CH 3 CN)] 2+ } (see Supplementary Fig. S11). See ref. S4 for the UV-vis and ESI MS of 4. References S1. Armarego, W. L. F.; Perrin, D. D., Eds. Purification of Laboratory Chemicals; 8 nature chemistry 8

9 Pergamon Press: Oxford, S2. Halfen, J. A.; Young, V. G., Jr. Chem. Commun. 2003, S3. Kieber-Emmons, M. T.; Annaraj, J.; Seo, M. S.; Van Heuvelen, K. M.; Tosha, T.; Kitagawa, T.; Brunold, T. C.; Nam, W.; Riordan, C. G. J. Am. Chem. Soc. 2006, 128, S4. Seo, M. S.; Kim, J. Y.; Annaraj, J.; Kim, Y.; Lee, Y.-M.; Kim, S.-J.; Kim, J.; Nam, W. Angew. Chem. Int. Ed. 2007, 46, S5. Evans, D. F. J. Chem. Soc. 1959, S6. Lölinger, J.; Scheffold, R. J. Chem. Edu. 1972, S7. Evans, D. F.; Jakubovic, D. A. J. Chem. Soc. Dalton Trans. 1988, S8. Sheldrick, G. M. SHELXTL/PC. Version 6.12 for Windows XP; Bruker AXS Inc.; Madison, WI, S9. Tenderholt, A. Pyspline and QMForge, S10. Rehr, J. J.; Albers, R. C. Rev. Mod. Phys. 2000, 72, S11. Rehr, J. J.; Mustre de Leon, J.; Zabinsky, S. I.; Albers, R. C. J. Am. Chem. Soc. 1991, 113, S12. Mustre de Leon, J.; Rehr, J. J.; Zabinsky, S. I.; Albers, R. C. Phys. Rev. B: Condens. Matter 1991, 44, S13. George, G. N. EXAFSPAK and EDG-FIT, S14. Neese, F. ORCA: an ab initio, DFT and semiempirical Electronic Structure Package., Version 2.4, Revision 16, S15. Neese, F.; Olbrich, G. Chem. Phys. Lett. 2002, 362, S16. Becke, A. D. Phys. Rev. A: At. Mol. Opt. Phys. 1988, 38, nature chemistry 9

10 S17. Becke, A. D. J. Chem. Phys. 1993, 98, S18. Perdew, J. P. Phys. Rev. B: Condens. Matter 1986, 33, S19. Sinnecker, S.; Slep, L. D.; Bill, E.; Neese, F. Inorg. Chem. 2005, 44, S20. Neese, F. Inorg. Chim. Acta 2002, 337, S21. Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, S22. Schaefer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, S23. Bergman, D. L.; Laaksonen, L. J. Mol. Graph. Model. 1997, 15, S24. Laaksonen, L. J. Mol. Graph. 1992, 10, S25. The Ni K-edge XAS spectrum of 2 has been previously published in (J. Am. Chem. Soc., 2006, 128, ). Due to large differences in the beamline optics, cryostat temperatures and detection methods, the data have been recollected for accurate comparison purposes. 10 nature chemistry 10

11 Table S1. Crystal data and structure refinements for 1-(ClO 4 ) CH 3 CN and 3-(ClO 4 ) 2. 1-(ClO 4 ) CH 3 CN 3-(ClO 4 ) 2 Empirical formula C 14 H 31 ClN 5 NiO 6 C 14 Cl 2 CoN 5 O 8 Formula weight Temperature (K) Wavelength (Å) Crystal system/space group orthorhombic, Pca2(1) tetragonal, P4/nmm Unit cell dimensions a (Å) (16) 8.969(3) b (Å) (6) 8.969(3) c (Å) (14) (11) (º) (º) (º) Volume (Å 3 ) (3) (11) Z 4 2 Calculated density (g/cm 3 ) Absorption coefficient (mm 1 ) Reflections collected Independent reflections [R(int)] 3915 [0.0420] 868 [0.1321] Refinement method Full-matrix least-squares on F 2 Full-matrix least-squares on F 2 Data/restraints/parameters 3915/1/ /0/58 Goodness-of-fit on F Final R indices [I > 2sigma(I)] R 1 = , wr 2 = R 1 = , wr 2 = R indices (all data) R 1 = , R 1 = , Largest difference peak and hole (e/å 3 ) wr 2 = wr 2 = and and nature chemistry 11

12 Table S2. Selected bond distances (Å) and angles (º) for 1-(ClO 4 ) CH 3 CN and 3-(ClO 4 ) 2. Bond Distances (Å) 1-(ClO 4 ) CH 3 CN 3-(ClO 4 ) 2 Ni-O (3) Ni-N (5) Ni-O (3) Ni-N (10) Ni-N (3) Ni-N (3) Ni-N (3) Ni-N (3) O1-O (4) Bond Angles ( ) 1-(ClO 4 ) CH 3 CN 3-(ClO 4 ) 2 O1-Ni-O (11) N1-Ni-N1_ (3) N1-Ni-N (12) N1-Ni-N1_ (7) N1-Ni-N (11) N1-Ni-N (14) N1-Ni-N (10) N2-Ni-N (12) N2-Ni-N (14) N3-Ni-N (12) 12 nature chemistry 12

13 Table S3. Ni-K Pre-edge Analysis. Pre-edge (1s 3d) (ev) Pre-edge Intensity b Ni K-edge Maxima (ev) (0.04) a 4.3(0.4) (0.02) 10.2(0.3) a Values in parentheses are the statistical standard deviations calculated from the individual acceptable fits used in the analysis. b The reported values are multiplied by 100 for convenience. 13 nature chemistry 13

14 Table S4. EXAFS Least Squares Fitting Results. Complex Coordination/Path R(Å) a 2 (Å 2 ) b E 0 (ev) F c 2 Ni-O Ni-N Ni-N Ni-C Ni-N/C-N/C d 6 Ni-N/C-N/C Ni-O Ni-N Ni-C Ni-C Ni-N/C-N/C a The estimated standard deviations for the distances are in the order of ± 0.02 Å. b The 2 values are multiplied by c Error is given by [( obsd calcd ) 2 k 6 ]/ [( obsd ) 2 k 6 ]. d The 2 factor of the multiple scattering path is linked to that of the corresponding single scattering path. 14 nature chemistry 14

15 Table S5. Selected DFT Parameters. Model Structural Parameters Mayer Bond-Order Mulliken Population Ni(O Total ) b Ni-O 1 (O 2) O 1-O 2 Ni-N 1 (N 2) a NiO 1O 2 NiN 1N 3 NiN 2N 4 Ni-O 1 O 1-O (1.88) (2.19) (55.5) 68.3 (2.1) 45.6 (43.2) (2.83) (2.17) (90.5) 47.5 (37.4) 71.9 (3.0) a The average of the trans Ni-N 1 (N 3 ) and Ni-N 2 (N 4 ) bond distances are represented by Ni-N 1 and Ni-N 2, respectively. b * 1, 2, and 3 represent the compositions of the LUMO, * LUMO and * LUMO +1 orbitals, respectively. 15 nature chemistry 15

16 Figure S1. (A) UV-vis spectrum of [Ni(12-TMC)(CH 3 CN)] 2+ (3) in CH 3 CN. (B) ESI MS of 3 in CH 3 CN. 16 nature chemistry 16

17 Figure S2. X-ray crystal structure of the [Ni(12-TMC)(CH 3 CN)] 2+ cation in 3-(ClO 4 ) 2 (gray C, blue N, green Ni). 17 nature chemistry 17

18 Figure S3. (A) ESI MS of [Ni(12-TMC)(O 2 )] + (1) in CH 3 CN at 0 o C. Inset shows observed isotope distribution patterns for [Ni(12-TMC)( 16 O 2 )] + (lower) and [Ni(12-TMC)( 18 O 2 )] + (upper). (B) X-band EPR spectrum of 1 (g values = 2.22, 2.17, 2.06) in frozen CH 3 CN at 4.3 K. Spectral conditions: microwave power = mw, frequency = 9.10 GHz, sweep width = 0.5 T, modulation amplitude = 0.2 mt. 18 nature chemistry 18

19 Figure S4. The k 3 weighted Ni K-edge EXAFS (inset) and their corresponding non-phase shift corrected Fourier transforms for 1( ) and 2( ). 19 nature chemistry 19

20 Figure S5. The k 3 weighted Ni K-edge EXAFS (inset) and their corresponding non-phase shift corrected Fourier transforms for 1. Data( ), Fit( ). 20 nature chemistry 20

21 Figure S6. The k 3 weighted Ni K-edge EXAFS (inset) and their corresponding non-phase shift corrected Fourier transforms for 2. Data( ), Fit( ). 21 nature chemistry 21

22 Figure S7. Schematic showing the geometry optimized structures of 1 (left) and 2 (right). 22 nature chemistry 22

23 Figure S8. Reactions of [Ni(12-TMC)(O 2 )] + (1) with 2-phenylpropionaldehyde (2-PPA) in CH 3 CN at 25 ºC. (A) UV-vis spectral changes of 1 (4 mm) upon addition of 40 equiv of 2- PPA. Inset shows the time course of the absorbance at 400 nm. (B) Plot of k obs against 2- PPA concentration to determine a second-order rate constant (k 2 = M 1 s 1 at 25 o C). 23 nature chemistry 23

24 Figure S9. Reactions of [Ni(12-TMC)(O 2 )] + (1) with cyclohexanecarboxaldehyde (CCA) in CH 3 CN at 10 ºC. (A) UV-vis spectral changes of 1 (4 mm) upon addition of 20 equiv of CCA. Inset shows the time course of the absorbance at 400 nm. (B) Plot of k obs against CCA concentration to determine a second-order rate constant (k 2 = 2.0 x 10-1 M 1 s 1 at 10 o C). 24 nature chemistry 24

25 Figure S10. Hammett plot for the oxidation of para-substituted benzaldehydes, para-y-ph- CHO (Y = Me, F, H, Br, Cl), by [Ni(12-TMC)(O 2 )] + (1) in CH 3 CN at 25 ºC. 25 nature chemistry 25

26 Figure S11. ESI MS taken after the completion of the O 2 -transfer reaction between 1 and 4 in CH 3 CN at room temperature: Mass peaks assigned to m/z of 343 for [Mn(14- TMC)(O 2 )] + (5) (see Seo, M. S.; Kim, J. Y.; Annaraj, J.; Kim, Y.; Lee, Y.-M.; Kim, S.-J.; Kim, J.; Nam, W. Angew. Chem. Int. Ed. 2007, 46, ), m/z of 143 for [Ni(12- TMC)] 2+ (3), m/z of 163 for [Ni(12-TMC)(CH 3 CN)] 2+ (3), and some impurities such as m/z of 176 for [Mn(14-TMC)] 2+ (4) and m/z of 257 for [14-TMC + H] nature chemistry 26

27 Figure S12. Reaction of [Ni(12-TMC)(O 2 )] + (1) and [Mn(14-TMC)] 2+ (4) in acetone. (A) UV-vis spectral changes of 1 (1 mm) upon addition of 10 equiv 4 at 50 ºC. Inset shows the time course of the absorbance at 453 nm. (B) Plot of k obs against the concentration of 4 to determine a second-order rate constant at 50 ºC. (c) Plot of first-order rate constants against 1/T to determine activation parameters for the reaction of 1 (1 mm) and 4 (10 mm). 27 nature chemistry 27